JWST Detects Water-Ice Clouds on Closest "Super-Jupiter" Exoplanet

Astronomers have directly imaged Epsilon Indi Ab, a cold gas giant with unexpected water-ice clouds. Discover how this find challenges current exoplanet models.

By: AXL Media

Published: Apr 22, 2026, 5:15 AM EDT

Source: Information for this report was sourced from EurekAlert!

A Direct Look at a Cold Giant

While the James Webb Space Telescope (JWST) has spent its first few years unveiling the atmospheres of scorching "Hot Jupiters," a new study led by the Max Planck Institute for Astronomy (MPIA) has successfully characterized a much rarer target: a cold, distant "Super-Jupiter." The planet, Epsilon Indi Ab, orbits a star slightly smaller than our Sun in the southern constellation Indus. Unlike most exoplanets discovered through indirect "wobbles" or transits, Epsilon Indi Ab was seen through direct imaging, a feat made possible by JWST’s Mid-Infrared Instrument (MIRI).

The Profile of a Solar System Cousin

Epsilon Indi Ab is a massive gas giant, weighing in at approximately 7.6 times the mass of Jupiter, though it maintains a nearly identical diameter. It sits four times further from its host star than Jupiter does from the Sun, making it a true solar-system analogue. Despite its distance, the planet is slightly warmer than Jupiter, with temperatures hovering between –70°C and +20°C. This relative warmth is a lingering "glow" from its birth billions of years ago; as the planet continues to age, it will eventually cool to match the frigid temperatures of our own outer planets.

Surprising Evidence for Water-Ice Clouds

To peer into the planet’s atmosphere, researchers utilized a coronagraph to block the blinding light of the host star. They measured the planet’s brightness at specific wavelengths to detect ammonia gas, a staple of gas giant atmospheres. However, the team found significantly less ammonia than expected. Lead author Elisabeth Matthews and her colleagues determined that the missing ammonia is likely masked by thick, patchy water-ice clouds similar to high-altitude cirrus clouds on Earth. This discovery was unexpected, as most current exoplanet models assume these cold worlds are cloud-free to simplify complex calculations.